FR2845418A1 - VARIABLE VALVE CONTROL DEVICE FOR INTERNAL COMBUSTION ENGINE - Google Patents

Abstract

Varying the actuation angle of the engine valves and the amount of valve lift depending on the engine operating conditions.The device includes a control shaft (32) provided to rotate in accordance with the engine operating conditions, an alteration mechanism (4) for changing the amount of lift and the actuation angle of the valves (2) of the engine in accordance with the rotation of the control shaft (32), and a drive mechanism (6 ) to rotate the drive shaft (32) and which includes an electric motor (36) and a reduction mechanism (37). The reduction mechanism has a reduction ratio set to be larger when the valve is under a low lift amount and low actuation angle control only when the valve is under the control of high lift amount and high actuation angle.

Description

The present invention relates to a variable control device for

  valves (CVS) for an internal combustion engine, this device being able to vary at least the actuation angle of the engine valves, such as an intake valve and an exhaust valve, in accordance with conditions of

engine operation.

  Typically, a CVS device applied to intake valves comprises a crankshaft cam 10 disposed at the outer periphery of a drive shaft which rotates in synchronism with a crankshaft and which has an eccentric axis relative to the axis of the drive shaft, and a valve actuating cam (AS) to which the torque of the crankshaft cam is transmitted by means of a transmission mechanism so that this cam has a face which comes into sliding contact with the upper face of a valve lifting member disposed at the upper end of the intake valve for its opening operation against the force of

  stress on a valve spring.

  The transmission mechanism comprises a rocker arm disposed above the AS cam and supported in an oscillating manner by a control shaft, a crankshaft arm having a first annular end engaged on the external peripheral surface of the crankshaft cam and a second end rotatably connected to a first arm of the rocker arm via a finger, as well as an articulated link 30 having a first end rotatably connected to a second arm of the rocker arm via 'a finger and a second end rotatably connected to a cam boss of the cam AS via a finger The control shaft is driven, for example, via an electric motor, via a worm gear or reduction mechanism provided on a motor drive shaft. Attached to the outer peripheral surface of the control shaft is a control cam whose axis is eccentric by a predetermined amount relative to the axis of the control shaft and which is rotatably mounted in a support hole formed substantially in the center of the rocker arm. The control cam modifies the center of tilting of the rocker arm in accordance with the rotational position in order to modify the contact position of the face of the cam AS relative to the upper face of the valve lifting member, by performing variable control of the lift quantity and the actuation angle of the intake valve. Specifically, when the operating conditions of the engine are in the low rotation range, for example, the control shaft is rotated in a certain direction through the motor in order to rotate the control cam in 20 in the same direction, by moving the center of rocking of the rocker arm in the direction of separation from the drive shaft. A pivot point of the rocker arm with the articulated link is then moved upward to pull the boss of the cam AS, 25 by moving the contact position of this cam by

  relative to the upper face of the valve lifting member in the direction of separation from the lifting part of the cam. The inlet valve is thus controlled to minimize the amount of lift and the actuation angle.

  On the contrary, when the operating conditions of the motor pass from the low rotation range to the high rotation range, the control shaft is caused by the motor to rotate in another direction in order to rotate the control cam in the same direction, by moving the center of tilting of the rocker arm in the approach direction of the drive shaft. The boss of the cam AS is then pushed downwards, in particular by the articulated link, in order to move the contact position of this cam relative to the upper face of the valve lifting member 5 to the lifting portion of drug. The intake valve is thus controlled to increase the amount of lifting and the actuation angle. It is therefore possible to obtain, in accordance with the operating conditions of the engine, very good engine performance such as better fuel consumption, greater

  motor output power, and the like.

  With the CVS device, however, and as will be seen later in connection with FIG. 8 of the appended drawings, the worm gear intended to reduce the rotation of the motor for the control of the control shaft presents a relationship. reduction which is always constant regardless of the conditions for controlling the amount of valve lift and the actuation angle. Thus, under a low valve lift and a weak control of the actuation angle, which corresponds to a control area in the ordinary drive range, i.e. the range of use practicality of the vehicle, the reduction ratio is lower, which leads to a more

  high engine power consumption.

  Specifically, the reduction ratio obtained from the angular speeds of the motor drive shaft and the control shaft corresponds to a torque ratio of the motor which is proportional to the current supplied to it. Therefore, under a low valve lift and a weak control of the actuation angle, the reduction ratio is not increased and is therefore lower, which leads to a greater torque of the motor to make turn the drive shaft. This increases the power consumption during ordinary vehicle driving, which results in a detrimental effect on the fuel consumption of the internal combustion engine which also serves to drive accessories such as an alternator. Furthermore, if the power supplied to the motor is lower due to a reduction in the storage capacity of the battery to supply power to the motor, a technical problem may occur such as a deterioration in the capacity of motor rotation

  within the normal drive range of the vehicle.

  In addition, since the reduction ratio is not decreased and is thus constant during the transition from a low valve lift to a high valve lift, which occurs for rapid acceleration of the vehicle and analogous, the total number of engine revolutions required for this transition cannot be decreased, causing a slower transition time, resulting in a possible lowering of the switching response of a low valve lift high valve lift. The object of the invention is therefore to create a CVS device for an internal combustion engine which allows a reduction in the power consumption of the engine under small amounts of lifting and actuation angle control, as well as an increase in the switching response when the command is switched from a small amount of lift and actuation angle control to high amounts of lift and actuation angle control. The present invention generally creates a variable valve control device (CVS) for an internal combustion engine comprising at least one valve, characterized in that it comprises: a control shaft intended to rotate in accordance with operating conditions. engine operation, an alteration mechanism which changes at least one actuation angle of the valve in accordance with the rotation of the control shaft, and a drive mechanism which rotates the control shaft, the mechanism drive comprising an electric motor and a reduction mechanism, the reduction mechanism having a reduction ratio set to be greater when the valve is under the control of a small actuation angle than when the valve is under the control control of a high actuation angle According to other advantageous features of the invention: - the reduction mechanism comprises an output shaft rel linked to the motor and having an engagement part at its external periphery; a movable member engaged with the engaging portion of the output shaft, the movable member moving in the axial direction of the output shaft in accordance with the rotation of the output shaft; an articulated element having a first end connected in an oscillating manner to the mobile element; and an articulation linked in an oscillating manner to a second end of the articulated element, the articulation rotating the control shaft due to the torque transmitted by the articulated element in accordance with the axial movement of the movable element, so that, when the valve is under the control of a small actuation angle, the angle formed between the articulated element and the output shaft is increased; - the alteration mechanism is rotated in synchronism with a crankshaft of the engine, the alteration mechanism comprising a drive shaft having, at its outer periphery, a crankshaft cam, a valve actuating cam 35 supported oscillatingly by a support shaft and having a face which comes into contact with an upper face of a valve lifting member for

_ 6

  perform the operations of opening and closing the valve, and a rocker arm having a first arm mechanically connected to the crankshaft cam and a second arm connected to the valve actuating cam by means of a articulated link, so that a center of tilting of the rocker arm is modified in accordance with the operating conditions of the engine to modify the contact position of the valve actuating cam relative to the upper face of the valve member. valve lift, thereby varying the valve lift; the output shaft of the reduction mechanism comprises a threaded shaft having an external thread formed on its external peripheral surface, the movable element comprising a threaded nut having an internal thread formed on its internal peripheral surface, the external thread being in taken with internal thread; the output shaft of the reduction mechanism 20 comprises a threaded shaft having a spiral ball groove formed in its external peripheral surface, the movable element comprising a threaded nut having a guide ball groove formed in its internal peripheral surface , so that the spiral ball groove cooperates with the guide ball groove to maintain a plurality of free rolling balls; the articulation of the reduction mechanism is fixed to the control shaft, a pivot point of the articulation with the articulated element being offset relative to the axis of the control shaft; - When the valve is under the control of a maximum actuation angle, the angle formed between the articulated element and the output shaft is minimum; when the valve is under the control of a minimum actuation angle, the angle formed between the articulated element and the output shaft is maximum; - a restriction mechanism is provided which limits the maximum axial movement of the mobile element; - The movable element is moved axially without being caused to rotate; - The reduction mechanism comprises an output shaft connected to the motor and having an engagement part at its external periphery; a movable member engaged with the engaging portion of the output shaft, the movable member moving in the axial direction of the output shaft in accordance with the rotation of the output shaft, the movable member comprising a finger, and an articulated lever having a first end fixed to the control shaft and a second end presenting a slot, the slot being engaged with the finger, the control shaft being driven in rotation by

  through the articulated lever in accordance with the axial movement of the movable member and, when the valve is under the control of a small actuation angle, the angle formed between the articulated lever and the output shaft is reduced .

  The invention will be better understood, and other aims,

  characteristics, details and advantages thereof will appear more clearly during the explanatory description which follows, given with reference to the appended drawings given solely by way of example illustrating a

  embodiment of the invention and in which: - Figure 1 is a longitudinal sectional view showing a first embodiment of a variable valve control device (CVS) for an internal combustion engine according to the present invention; - Figure 2 is a perspective view showing the CVS device; FIGS. 3A and 3B are views according to arrow A in FIG. 2 showing respectively the valve closing operation and the valve opening operation during a minimum lift command; - Figures 4A and 4B are views similar to Figure 3B, according to arrow A in Figure 2, respectively showing the valve closing operation and the valve opening operation during a medium lift command; FIGS. 5A and 5B are views similar to FIG. 4B, according to arrow A in FIG. 2, showing respectively the valve closing operation and the valve opening operation during a maximum lifting command; - Figure 6 is a view similar to Figure 1 for explaining the operation of a drive mechanism during a minimum lift command; Figure 7 is a sectional view taken along the line VII-VII of Figure 1; - Figure 8 is a graph illustrating the characteristic of the amount of valve lift as a function of the reduction ratio; Figure 9 is a view similar to Figure 6 showing a second embodiment of the present invention; and - Figure 10 is a graph similar to the

  Figure 6 illustrates the characteristic of the amount of valve lift as a function of the reduction ratio in the second embodiment.

  Referring now to the drawings, there will be described a variable valve control device (CVS) for an internal combustion engine embodying the present invention. In the illustrated embodiments, the CVS device is applied to

  an internal combustion engine comprising two intake valves per cylinder, the amount of valve lift and the actuation angle of each of them being modified in accordance with the operating conditions of the engine.

  Referring to Figures 2 to 5B, there is shown a first embodiment of the present invention. The CVS device comprises a pair of intake valves 2 intended to slide on a cylinder head 1 via valve guides, not shown, and biased in the direction closed by 5 of the valve springs 3, a mechanism for alteration for

  vary the amount of lift of the intake valves 2, a control mechanism 5 for controlling the operating position of the alteration mechanism 4, and a drive mechanism 6 for driving the control mechanism 5.

  The alteration mechanism 4 comprises a hollow drive shaft 13 rotatably supported by a bearing 14 in an upper part of the cylinder head 1, a crankshaft or eccentrically rotatable cam 15 fixed to the shaft. drive 13 by press fit or the like, a pair of valve actuating cams (AS) 17 supported in an oscillating manner on the outer peripheral surface of the drive shaft 13 and coming into sliding contact with lifting devices of valve 16 arranged at the upper ends of the intake valves 2 for their opening operation, and a transmission mechanism connected between the crankshaft cam 15 and the cams AS 17 for transmitting the torque from the crankshaft cam 15 to the cams AS 17 as an oscillation force thereof Referring to Figure 2, it can be seen that the drive shaft 13 extends along the longitudinal direction of the motor and that it has an e end 30 provided with a follower pinion, a synchronization chain wound on it, etc., not shown, by means of which a torque is received from a crankshaft of the engine. The drive shaft 13 is rotated in a clockwise direction, i.e. in the direction of the arrow

shown in Figure 2.

  Referring to FIG. 3A, it can be seen that a bearing 14 comprises a main console 14a disposed at the upper end of the cylinder head 1 for supporting an upper part of the drive shaft 13 and an auxiliary console 14b disposed at the upper end of the main console 14a to support in rotation a control shaft 32 as will be described later. The brackets 14a, 14b are interconnected

  from above using a pair of 14c bolts.

  The crankshaft cam 15 is formed in a manner practically analogous to a ring and comprises a main annular body and a cylinder which is integral with its external end face. A through hole is formed along the axis of the cam

  crankshaft 15 to receive the drive shaft 13.

  Referring to FIGS. 3A to 5B, it can be seen that an axis Y of the main body of the crankshaft cam 15 is offset radially by a predetermined quantity P relative to an axis X of the drive shaft 13. The crankshaft cam 15 is fitted snug on one end of the drive shaft 13 through the through hole of the shaft 15 so as not to interfere with the valve lift members 16. A cam profile in eccentric circle is formed on the surface

  external device of the main body of the cam.

  The valve lifting members 16 have a shape similar to a covered cylinder, each being held in a sliding manner in a hole in the cylinder head 1 and having a flat upper face with which the cam AS 17 comes into sliding contact. Referring to Figures 2 to 3B, the cams AS 17 are both formed substantially in a manner similar to a raindrop and they are integrated at both ends of an annular crankshaft 20 having an internal peripheral surface through which it is supported in rotation by the drive shaft 13. The cam AS 17 also has a finger hole on the side of one end or boss 21 of the cam. A lower face of the cam AS 17 has a face 22 including a face with a circular base on the side of the crankshaft 20, 5 an inclined face extending in a circular manner from the face with a circular base to the boss 21 of the cam, and a lifting face extending from the inclined face to an upper face with a maximum lifting provided at one end of the boss 21 of the cam. The face with circular base, the inclined face, and the lifting face come into contact with predetermined points on the upper face of the valve lifting member 16 in accordance with the position.

oscillation of the cam AS 17.

  Referring to FIGS. 2 to 5B, it can be seen that the transmission mechanism 18 comprises a rocker arm 23 arranged above the drive shaft 13, a crankshaft arm 24 for connecting a first arm 23a of the arm of rocker arm 23 with crankshaft cam 15 15 and an articulated link 25 to connect a second

  arm 23b of the rocker arm 23 with the cam AS 17.

  The rocker arm 23 has at its center a cylindrical base rotatably supported by a control cam 33, as will be described later, through a support hole. The first arm 23a, which projects from the outer end of the cylindrical base, has a finger hole for receiving a finger 26, while the second arm 23b, which projects from the inner end of the cylindrical base, has a finger hole for receiving a finger 27 making it possible to connect the second arm 23b and a first end 25a of the link

articulated 25.

  The crankshaft arm 24 incorporates an annular base 24a of relatively large diameter and an extension 24b provided in a predetermined position of the outer peripheral surface of the base 24a. the base 24a has in its center an engagement hole 24c rotatably engaged with the main body of the crankshaft cam 15. The extension 24b has a

  finger hole for rotationally receiving the finger 26.

  The articulated link 25 has substantially the shape of the letter L with a concave part on the side of the rocker arm 23, and has first and second ends 25a, 25b with finger holes through which the ends are rotatably arranged. of fingers 27, 28 fitted tightly in 10 the corresponding finger holes of the second arm 23b of the

  rocker arm 23 and boss 21 of the cam AS 17.

  Arranged at one end of the fingers 26, 27, 28, are

  find snap rings to limit the axial movement of the crankshaft arm 24 and the articulated link 25.

  The control mechanism 5 comprises a control shaft 32 disposed above the drive shaft 13 and rotatably supported by bearings 14, as well as a control cam 23 fixed to the outer periphery 20 of the drive shaft. command 32 to constitute a

  tilt center for the rocker arm 23.

  As can be clearly seen in FIG. 2, the control shaft 32 is arranged parallel to the drive shaft 13 to extend along the longitudinal direction of the motor, and it comprises, in a predetermined position, a pin 32b rotatably supported between the main console 14a and the

  auxiliary console 14b of the bearing 14.

  Referring to Figures 2 to 5B, the control cam 33 has a shape similar to a cylinder and has its axis P2 offset from the axis P1 of the control shaft 32 by an amount ax corresponding to

a thick portion.

  Referring to Figures 1, 2, 6 and 7, the drive mechanism 6 comprises a housing 35 fixed to the rear end of the cylinder head 1, an electric motor constituting a means supplying a torque 36 fixed to a end of the housing 35, and a screw transmission mechanism constituting a reduction mechanism or means 37 arranged in a housing 35 to reduce the torque of the motor and transmit it to the control shaft 32. The housing 35 comprises a cylindrical part 35a disposed along a direction substantially perpendicular to the axis P1 of the control shaft 32, an enlarged portion 35b projecting upward relative to the center of the upper end of the cylindrical portion 35a, and a side wall 35c to close one side of the cylindrical part 35a and the enlarged part b. The motor 36 consists of a proportional type direct current motor 15 and comprises a casing 38 having, at one end, a portion 38a of small diameter engaged in a first opening 35c of the cylindrical part 35a by a tight fitting assembly. or the like, and a drive shaft 36a supported by a ball bearing 39 disposed in the portion of small

diameter 38a.

  It will also be noted that the motor 36 is driven

  in accordance with a control signal from an electronic control unit (ECU) 40 for determining the operating conditions of the engine.

  The electronic control assembly 40 receives detection signals from a crankshaft angle sensor 41 to detect the engine speed, from an air flow measurement member 42 to detect the amount of intake air, a coolant temperature sensor 43 to detect the engine coolant temperature, and a potentiometer 44 to detect the rotational position of the control shaft 32 to determine the actual conditions of engine operation using a calculation or the like, thereby effecting a feedback control

motor 36.

  Referring to Figures 1, 6 and 7, it can be seen that the screw transmission mechanism 37 essentially comprises a threaded shaft constituting an output shaft 45 disposed in the cylinder 35a of the housing 35 so as to be roughly coaxial with the shaft d drive 36a of the motor 36, a threaded nut constituting a movable element 46 engaged with the external periphery of the threaded shaft 45, an articulated arm constituting a joint 47 arranged in the housing 35 and fixed to the external periphery 10 of a end of the control shaft 32, and an articulated element 48 for connecting the articulated arm 47 to

the threaded nut 46.

  The threaded shaft 45 has an external thread constituting an engagement part 49 formed continuously over the entire external peripheral surface with the exception of the ends 45a, 45b which are directed towards first and second openings 35c, 35d of the cylinder. 35a to be supported in rotation by

ball bearings 50, 51.

  A nut 52 is engaged with a tip of a second

  end 45b of the threaded shaft 45 to hold the threaded shaft 45 in the cylindrical part 35a of the housing 35.

  The nut 52 has at one end a projection 52a designed to push an inner ring 51a of the ball bearing 51 against a stepped part of a second

  end 45b of the threaded shaft 45 for its attachment.

  The nut 52 is rotated at the same time as the threaded shaft 45. A cap 53 is fixed to a second opening 35d of the cylindrical part 35a and 30 has a cylindrical front end through which an outer ring 51b of the bearing to balls 51 is pushed and fixed on a stepped part 35f of the second

opening 35d.

  Two engagement faces 45d are formed in the second end 45b of the threaded shaft 45, a holding assembly being engaged to prevent rotation of the threaded shaft 45 when the nut 52 is tightened by a

  specific tool such as a screw wrench.

  The threaded shaft 45 has, at a first end 45a, a small diameter shaft 45c coupled by 5 notches coaxially to a small diameter portion 36b of the drive shaft 36a of the motor 36 via an element cylindrical coupling 54

in order to be axially movable.

  Specifically, first notches are formed axially on the outer peripheral surfaces of the small diameter shaft 45c and of the small diameter portion 36b, while a second notch is formed on the inner peripheral surface of the element. coupling 54 to engage loosely with the first 15 notches. Such a notched coupling allows the transmission of the torque from the motor 36 to the threaded shaft 45

  as well as a slight axial movement of the threaded shaft 45.

  The threaded nut 46, which has substantially the shape of a cylinder, has over its entire internal peripheral surface 20 an internal thread 55 in engagement with the external thread 45 to convert the torque of the threaded shaft 45 into a force of movement axial, and it also has at its two ends, substantially in its central axis, finger holes 56 provided to extend along the diametrical direction, as shown in the

figure 7.

  Referring to Figures 1 and 2, it can be seen that the articulated arm 47, which has substantially the shape of a raindrop, has a fixing hole 47a formed through a base of large diameter to receive a

  end 32a of the control shaft 32, and that it is fixed to one end 32a by a bolt, not shown.

  As can be seen in FIGS. 6 and 7, the articulated arm 47 has a frustoconical end 47b with a slot 57 made in the center in its transverse direction. Two finger holes 47c are formed through the end 47b to extend continuously in the direction of the drive shaft 32. As a result, the Z axis of the finger holes 47c is offset from the tree axis Pi

32.

  Referring to FIG. 7, it can be seen that the articulation element 48 has substantially the shape of the letter Y and that it has a first flat end 58 and a second end forming a fork 59. The first end 58 is mounted through the slot 57 of the articulated arm 47 to be rotatably coupled to the end 47b of the articulated arm 47 by a finger 60 mounted through the finger holes 47c and the finger hole 58a. Furthermore, the second ends 59 are arranged at the two ends of the threaded nut 46 and are rotatably coupled to the threaded nut 46 via oppositely formed finger holes 59a and finger shafts 61 mounted through the finger holes 56 of the threaded nut 46. The finger 60 has its two ends engaged in the finger holes 47c of the articulated arm 47 and its central part slidably mounted in the finger hole 48a of the element

  hinged 48. Furthermore, the finger shafts 61 have their outer ends fitted with press fit in the finger holes 59a of the articulated element 48, and their internal ends slidably mounted 25 in the finger holes 56 of the threaded nut 46.

  Referring to Figures 1 and 6, it can be seen that first and second stop fingers forming a limiting mechanism 62, 63 are mounted inside a side wall 35e of the housing 35 to limit the maximum position of rotation. right-left of the control shaft

  32 via the articulated arm 47.

  Specifically, a first stop finger 62 is fixed in the position of the side wall 35e o the control shaft 32 is caused to rotate anti-clockwise as seen in the figure 1 to minimize the amount of intake valve 2 by means of the alteration mechanism 4. Furthermore, a second stop finger 63 is fixed in the position of the side wall 35e o the control shaft 32 is rotated clockwise as shown in Figure 5 1 to set the amount of valve lift to a maximum. The first and second stop fingers 62, 63

  serve to limit the maximum positions of rotation anticlockwise and clockwise with respect to the control shaft 32.

  In the position o the control shaft 32 has its rotation limited by the first stop finger 62 via the articulated arm 47 as shown in Figure 6, that is to say in the position o the mechanism 15 alteration 4 keeps the amount of lift of the intake valves 2 to a minimum by means of the drive mechanism 6, the angle 01 formed between the axis of the articulated element 48 and the axis of the threaded shaft 45 is at a maximum value of about 650. When the control shaft 32 is rotated clockwise as shown in Figure 1 to control the amount of valve lift to a maximum o a subsequent rotation of the control shaft 32 is limited by the second stop finger 63, 25 an angle 03 formed between the axis of the articulated element 48 and the axis of the threaded shaft 45 is at a minimum value

about 350.

  Consequently, with reference to FIG. 8, it can be seen that the reduction ratio of the screw transmission mechanism 37 with respect to the rotation of the motor 36 varies the angle 0 formed between the axis of the threaded shaft 45 and the axis of the articulated element 48 as shown by a dashed line. Specifically, as shown by the solid line, the reduction ratio is greater when the angle 0 takes the maximum value 01 at the minimum lift, and it becomes abruptly small from there to a

  minimum angle 03 at the maximum lift.

  More specifically, the reduction ratio is determined by the angular speeds of the threaded shaft 45 and the control shaft 32 as described above. In the area of low lift where the angle 0 is greater, the axial movement of the threaded nut 46 is not effectively converted into rotation of the control shaft 32 due to the relationship with the articulated element 10 48, which makes it possible to obtain a greater

  reduction ratio. Furthermore, in the high lifting zone where the angle 0 is smaller, the axial movement of the threaded nut 46 is effectively converted into rotation of the control shaft 32, which makes it possible to obtain a lower reduction ratio.

  The operation of the first embodiment

is described below.

  In the low rotation operating range of the engine, which includes idling, the torque 20 supplied to the engine 36 in accordance with a control signal from the electronic control assembly 40 is transmitted to the threaded shaft 45 for its rotation. This rotation moves the threaded nut 46 to the rightmost position as shown in Figure 6, so that the control shaft 32 is caused to rotate counterclockwise by the element articulated 48 and articulated arm 47. Immediately before the lateral face of the threaded nut 46 comes into impact and in axial engagement, the lateral face of the end 47b of the articulated arm 47 abuts against the stop finger 62 to limit the additional rotation of the control shaft 32. At this time, it is possible to avoid the occurrence of an impact load at a portion in engagement of the threaded nut 46 and 35 of the threaded shaft 45 while setting a range of mobility

of the threaded nut 46.

  With the control cam 33, therefore, the axis P2 is caused to rotate on the same radius around the axis Pi of the control shaft 32 as shown in Figures 3A and 3B, making the thick portion be displaced 5 upward relative to the drive shaft 13. A pivot point of the second arm 23b of the rocker arm 23 with the articulated link 25 is thus displaced upward relative to the drive shaft 13 , so that the cam AS 17, the boss 21 of which is forcibly pulled upwards by means of the articulated link 25, is as a whole driven in

  clockwise rotation.

  Consequently, when the rotation of the crankshaft cam 15 pushes the first arm 23a of the rocker arm 23 upwards via the crankshaft arm 24, the corresponding amount of lift Li of the valves, transmitted to the cam AS 17 and to the valve lifting member 16 via the

  articulated link 25, is sufficiently weak.

  Thus, in the low rotation range of the engine, the amount of valve lift is minimum in order to delay an opening synchronization of the intake valves 21, allowing to obtain a smaller overlap of these valves with the valves 25 exhaust. This leads to better consumption

  fuel and more stable engine rotation.

  When the motor passes over the medium rotation range, the motor 36 is rotated in the opposite direction in accordance with a control signal from the electronic control assembly 40 to provide torque to the threaded shaft 45 so that he turns. This rotation moves the threaded nut 46 to the left from the position shown in Figure 6. Therefore, the control shaft 32 rotates the control cam 33 clockwise from the position shown in Figures 3A and 3B to rotate the axis P2 slightly downward as shown in Figures 4A and 4B. As a result, the rocker arm 23 is as a whole moved in the direction of the drive shaft 13, so that the second arm 23b pushes the boss 21 of the cam AS 17 5 downwards via of the articulated link, by rotating the cam AS as a whole by a predetermined amount in the opposite direction of the

Clockwise.

  Therefore, when the rotation of the crankshaft cam 15 pushes the first arm 23a of the

  rocker 23 upwards via the crankshaft arm 24, a corresponding quantity L2 of valve lift, transmitted to the cam AS 17 and to the valve lift member 16 via 15 the articulated link 25 , is relatively high.

  The reduction ratio is at this time slightly

  smaller than that in the minimum lift area.

  However, since the angle 0 formed between the threaded shaft 45 and the articulated element 48 is relatively large, the reduction ratio is also large, which makes it possible to obtain a low power consumption. When the motor changes to the high rotation range under rapid acceleration or the like, the motor 36 is again rotated in the opposite direction in accordance with a control signal from the electronic control assembly 40 which detects this state of operation by means of various sensors, such as the engine speed sensor 41, still rotating the threaded shaft 45 in the same direction. This rotation moves the threaded nut 46 to the left as shown in the figure 1, so that the angle 0 formed between the threaded shaft 45 and the articulated element 48 is sufficiently small. Furthermore, at this moment, immediately before the lateral face of the threaded nut 46 comes into impact and in axial engagement, an additional rotation of the control shaft 32 is limited in the position where the lateral face of the articulated arm 47 abuts against the second stop finger 63. Damage to the threaded nut 46 due to an impact can also be prevented while fixing a range of mobility for the threaded nut 4. Additional movement of the threaded nut 46 is also also limited, so that the angle 03 formed between

  the threaded shaft 45 and the articulated element 48 is minimum.

  With such an operation, the control shaft 32 rotates the control cam 33 clockwise from the position shown in Figures 4A and 4B to rotate the axis P2 downward as shown in Figures SA and 5B. As a result, the rocker arm 23 is moved as a whole in the direction of the drive shaft 13, so that

  the second arm 23b pushes the boss 21 of the cam AS 17 downwards by means of the articulated link 25, by rotating the cam AS 17 as a whole by a predetermined amount in the opposite direction to the needles a watch.

  Consequently, the contact position of the face 22 of the cam AS 17 relative to the upper face of the valve lifting member 16 is moved to the right, that is to say in the direction of the portion of 25 lifting. As a result, when the rotation of the

  crankshaft cam 15 pushes the first arm 23a of the rocker arm 23 via the articulated link 24, a corresponding amount of lift L3 relative to the valve lift member 16 is higher than the average amount L2 valve lift.

  Thus, in the high rotation range of the engine, the amount of valve lift is maximum in order to advance an opening synchronization and delay a closing synchronization of the intake valves 2, 35 while leading to increasing the charging efficiency. inlet air and therefore to obtain, for the engine, a power

sufficient output.

  As described above, in a small predetermined area of minimum lift or more intake valves which corresponds to the practical range of the vehicle, the reduction ratio of the screw transmission mechanism 37 is sufficiently large, leading to a reduction in the torque of the motor 36 required to rotate the control shaft 32 by means of the threaded nut 46 and of the articulated element assembly 48 - articulated arm 47. This allows a sufficient reduction in consumption engine 36, having no detrimental effect on the fuel consumption of the engine which also serves to

  drive accessories, such as an alternator.

  In addition, due to the lack of reduction in the amount of storage of a battery intended to supply power to the motor 36, it is possible to fix the power supply to the motor 36, avoiding deterioration of the rotation capacity of the motor 36

  within the normal drive range of the vehicle.

  In addition, during the transition between the low lift zone of the intake valves 2 and their high lift zone, the reduction ratio of the screw transmission mechanism 37 is lower, so that it is possible to reduce the total number of engine revolutions 36 required for this transition, thereby reducing the transition time, thereby preventing deterioration of the switching response between low valve lift and high valve lift. Additionally, in the first embodiment, first and second stop fingers 62, 63 are provided to prevent excessive rotation of the control shaft 32, not only allowing limitation of the unidirectional load input of the 35 alternating torque by the stop fingers 62, 63 in the rightmost and leftmost displacement positions of the threaded nut 46, but also a movement

excessive thread nut 46.

  It is also possible to prevent an impact load from occurring at a grip portion of the threaded nut 46 and of the threaded shaft 45 while fixing a range of mobility of the threaded nut. 46 using

stop fingers 62, 63.

  The nut 52 is further engaged with the second end 45b of the threaded shaft 45 to hold the inner ring 51a of the ball bearing 51 between the stepped portions of the threaded shaft 45 allowing limitation of axial movement accidental of the threaded shaft 45 while maintaining its stable and uniform rotation. Referring to Figure 9, we showed a second

  Embodiment of the present invention in which the screw transmission mechanism 37 includes no articulated member 47 or articulated arm 47, but an articulated lever 70 in place of the articulated arm 47, which is directly connected to the threaded nut 46.

  Specifically, the articulated lever 70 is formed in a similar manner to an axially long raindrop and its base 70a is fixed to one end 32a of the control shaft 32, a slot 71 25 being longitudinally formed substantially in the center of a tip 70b extending under one side of the threaded nut 46. Furthermore, the threaded nut 46 has a transmission finger 72 rotatably mounted substantially in the axial center on one side. Transmission finger

  72 has its base end rotatably supported in a support hole formed radially in the threaded nut 46, and a tip having two engagement faces 72a, 72b slidably engaged in the slot 35 71.

  When the articulated lever 70 is placed perpendicular (about 900) to an axis of the threaded shaft 45 as shown by the solid line in Figure 9, it abuts against the second stop finger 63 to limit rotation additional counterclockwise where maximum lift control is obtained through the control shaft 32. Thus, the angle of the articulated lever 70 relative to the threaded shaft 45 is set to be maximum (around 906) in the high lift zone, reaching a minimum reduction ratio 10. Note that such a wide angle allows the movement of the threaded nut 46 to be effectively

  converted into rotation of the articulated lever 70.

  Furthermore, when the articulated lever 70 is inclined at a predetermined angle (approximately 450) relative to the threaded shaft 45, as shown by the dashed line in Figure 9, it abuts against the first finger stop 62 to limit an additional rotation in a clockwise direction, where a minimum lift command is obtained. 20 Thus, the angle of the articulated lever 70 relative to

  the threaded shaft 45 is adjusted to be minimum (about 450) in the high lifting zone, reaching a maximum reduction ratio. It will be noted that such a small angle allows the movement of the threaded nut 46 to be effectively converted into rotation of the articulated lever 70.

  In the second embodiment, therefore, when the threaded shaft 45 is rotated in the normal direction or in the opposite direction by the motor 36 in order to linearly move the threaded nut 46 in the axial direction of the threaded shaft 45, the articulated lever is rotated in the same direction by the movement of the transmission finger 72 in the slot 71. Because of this, the control shaft 32 is rotated in the direction clockwise or counterclockwise to control the amount of lift and the actuation angle of the intake valves 2. Referring to Figure 10, it can be seen that the reduction ratio is greater in the low lift zone, making it possible to obtain a lower power consumption for the motor 36. On the contrary, the reduction ratio is smaller in the high lift zone, allowing 'get a better switching response via the alteration mechanism 4 and the control shaft 32 even with greater

power consumption.

  Therefore, the second embodiment not only produces the same effect as the first embodiment, but also achieves an improvement in manufacturing and assembly efficiency and, thus, a reduction in the cost of 15 manufacturing due to a reduction in the constituent parts and a simplification of the structure by

  compared to the first embodiment.

  In the above embodiments, the threaded shaft 45 of the screw transmission mechanism 37 has an external thread 49 formed on its outer peripheral surface, while the threaded nut 46 has an internal thread 55 formed on its surface internal peripheral, the external thread 49 being engaged with the internal thread 55. Optionally, the threaded shaft 45 may have a spiral ball groove formed on its external peripheral surface, while the threaded nut 46 may have a guide ball groove formed on its inner peripheral surface, the spiral ball groove cooperating with the guide ball groove to maintain a plurality of free rolling balls. In this variant, the use of the balls as a means for driving the threaded nut 46 makes it possible to increase the response to displacement and to reduce the play of the threaded nut 46 compared to a simple engagement of the external threads and internal 49, 55. As described above and as indicated in the preamble of this specification, during a small amount of valve lift and a small actuation angle control in the low rotation range of the engine, by example, which corresponds to the practical range of use of the vehicle, the reduction ratio is greater and, thus, the engine torque is smaller, allowing a reduction in the

  engine power consumption.

  On the contrary, when the engine changes from the low rotation range to the high rotation range due to rapid acceleration or the like, i.e. the control is changed to the high amount of valve lift and angle of actuation control, the reduction ratio during transition is more

  low and thus the torque of the motor is greater, which makes it possible to obtain a better switching response, even with greater power consumption of the motor. This results in an increase in vehicle acceleration performance.

  Furthermore, in accordance with the invention and as further indicated in the preamble of this specification, when the valve is under a control of small actuation angle, the angle formed between the articulated element and the shaft output of the reduction mechanism is increased. Thus, the angle of rotation of the articulation connected to the second end of the articulated element, that is to say the angle of rotation of the control shaft, is reduced compared to an actual number of 30 turns of the output shaft driven in rotation by the motor. Thus, the reduction ratio is greater, resulting in lower engine torque and

  therefore its power consumption.

  On the contrary, when the control is changed from the control of small actuation angle to the control of high actuation angle, the angle formed between the articulated element and the output shaft of the reduction mechanism is reduced . The reduction ratio is thus smaller, that is to say that the angle of rotation of the control shaft is larger, which makes it possible to obtain a better rotation response of the joint, c that is to say the switching response via the control shaft even with greater motor torque. This results in an increase in vehicle acceleration performance. It will further be noted that, as indicated above, the output shaft of the reduction mechanism may comprise a threaded shaft having a spiral ball groove formed in its external peripheral surface, and that the movable element may comprise a nut 15 threaded having a guide ball groove formed in its inner peripheral surface, so that the spiral ball groove cooperates with the guide ball groove to hold a plurality of balls

free rolling.

  The use of balls as a means for driving the movable element makes it possible to increase the response to displacement and to reduce the play of the movable element compared to a simple engagement of the external threads.

and internal.

  It will also be noted that, when the valve is under the control of a maximum actuation angle, the angle formed between the articulated element and the output shaft is minimum, so that it is possible to obtain a maximum reduction effect on a radial load acting on the movable member during a maximum actuation angle control having a larger entry, resulting in increased durability of the engaging portion of the drive shaft exit and

the movable element.

  Likewise, when the valve is under the control of a minimum actuation angle, the angle formed between the articulated element and the output shaft is maximum, so that it is possible to increase the ratio of reduction whereas, since it is involved in the zone of weak lifting having a smaller entry, it is possible to reduce a radial load 5 although the angle formed between the articulated element and the output shaft is larger, having no detrimental effect on the engaging portion of the output shaft and

of the movable element.

  As seen above, the device according to the invention advantageously comprises a restriction mechanism which limits the maximum axial movement of the mobile element, so that the position of maximum movement of the mobile element is limited by the restriction mechanism immediately before the movable element 15 comes into axial impact, making it possible to avoid the appearance of an impact load at the level of the engaging part of the output shaft and the moving element all

  by fixing a range of mobility of the mobile element.

  Likewise, the movable member is advantageously moved axially without being caused to rotate so that the movable member is in a state of non-rotation, allowing efficient torque conversion

  of the output shaft in an axial displacement force.

  Furthermore, and in accordance with the second embodiment of the invention, an increase is obtained

  in manufacturing and assembly efficiency and, thus, a reduction in manufacturing costs due to a smaller number of constituent parts and a simplified structure compared to the invention according to the first mode of production.

  The invention is not limited to the embodiments shown and described in detail since various modifications can be made thereto without departing from its scope. For example, the arrangement of the engine 36 can be freely modified according to the layout of the engine compartment, that is to say it can be changed on the right side to be brought

  on the left side according to FIG. 2. The present invention can also be applied to exhaust valves and, at the same time, to intake valves and to exhaust valves.

Claims (14)

  1. Variable valve control device for an internal combustion engine comprising at least one valve, characterized in that it comprises: a control shaft intended to rotate in accordance with operating conditions of the engine; an alteration mechanism which changes at least one actuation angle of the valve in accordance with the rotation of the drive shaft; and a drive mechanism which rotates the drive shaft, the drive mechanism comprising an electric motor and a reduction mechanism, the reduction mechanism having a reduction ratio set to be larger when the valve is under control of a small actuation angle only when the valve is under the   control of a high actuation angle.   2. Device according to claim 1, characterized in that the reduction mechanism comprises: an output shaft connected to the motor and having an engagement part at its external periphery; a movable member engaged with the engaging portion of the output shaft, the movable member moving in the axial direction of the output shaft in accordance with the rotation of the output shaft; an articulated element having a first end connected in an oscillating manner to the mobile element; and an articulation connected in an oscillating way to a second end of the articulated element, the articulation turning the control shaft due to the torque transmitted by the articulated element in accordance with the axial movement of the movable element, and in this that when the valve is under the control of a small actuation angle, the angle formed between the articulated element and the output shaft is increased. 3. Device according to claim 1, characterized in that the alteration mechanism is rotated in synchronism with a crankshaft of the engine, the alteration mechanism comprising a drive shaft having, at its outer periphery, a cam of a crankshaft, a valve actuating cam supported in an oscillating manner by a support shaft 10 and having a face which comes into contact with an upper face of a valve lifting member for carrying out the opening and closing operations of the valve, and a rocker arm having a first arm mechanically connected to the crankshaft cam and a second arm connected to the valve actuating cam via an articulated link, and in that a rocker arm tilt center is changed according to engine operating conditions to change the contact position of the valve actuating cam relative port on the upper face of the valve lifting member,   thereby varying the valve lift.   4. Device according to claim 2, characterized in that the output shaft of the reduction mechanism 25 comprises a threaded shaft having an external thread formed on its external peripheral surface, the movable element comprising a threaded nut having an internal thread formed on its internal peripheral surface, the external thread being engaged with the internal thread. 30 5. Device according to claim 2, characterized in that the output shaft of the reduction mechanism comprises a threaded shaft having a spiral ball groove formed in its external peripheral surface, the movable element comprising a threaded nut having a guide ball groove formed in its inner peripheral surface, so that the spiral ball groove cooperates with the guide ball groove for   maintain a plurality of free rolling balls.   6. Device according to claim 2, characterized in that the articulation of the reduction mechanism is fixed to the control shaft, a pivot point of the articulation with the articulated element being offset by   relative to the axis of the control shaft.   7. Device according to claim 2, characterized in that, when the valve is under the control of a maximum actuation angle, the angle formed between   the articulated element and the output shaft is minimum.   8. Device according to claim 2, characterized   in that, when the valve is under control of a minimum actuation angle, the angle formed between the articulated member and the output shaft is maximum.   9. Device according to claim 2, characterized in that it further comprises a restriction mechanism which limits the maximum axial movement of the movable element. 10. Device according to claim 2, characterized in that the mobile element is moved   axially without having to rotate.   11. Device according to claim 1, characterized in that the reduction mechanism comprises: an output shaft connected to the motor and having an engagement part at its external periphery; a movable member engaged with the engaging portion of the output shaft, the movable member moving in the axial direction of the output shaft 30 in accordance with the rotation of the output shaft, the movable member comprising a finger; and an articulated lever having a first end fixed to the control shaft and a second end having a slot, the slot being engaged with the finger, in that the control shaft is rotated by means of the lever articulated in accordance with the axial movement of the movable element, and in that, when the valve is under the control of a small actuation angle, the angle formed between the   movable lever and the output shaft is decreased.   12. Variable valve control device for an internal combustion engine comprising at least one valve, characterized in that it comprises: a control shaft intended to rotate in accordance with operating conditions of the engine; an alteration mechanism which changes at least one actuation angle of the valve in accordance with the rotation of the drive shaft; and a drive mechanism which rotates the drive shaft, the drive mechanism comprising an electric motor and a reduction mechanism, the reduction mechanism having a reduction ratio set to be larger when the valve is under the control of a small actuation angle only when the valve is under the control of a high actuation angle, the reduction mechanism comprising an output shaft connected to the motor and having an engagement part at its periphery external, a movable member engaged with the engaging portion of the output shaft, the movable member moving in the axial direction of the output shaft in accordance with the rotation of the output shaft; an articulated element having a first end connected in an oscillating manner to the mobile element; and an articulation linked in an oscillating manner to a second end of the articulated element, the articulation 35 rotating the control shaft due to a torque transmitted by the articulated element in accordance with the axial movement of the mobile element, and in that, when the valve is under the control of a small actuation angle, the angle formed between   the articulated element and the output shaft is increased.   13. Variable valve control device 5 for an internal combustion engine comprising at least one valve, characterized in that it comprises a control shaft intended to rotate in accordance with operating conditions of the engine; an alteration mechanism which changes at least one actuation angle of the valve in accordance with the rotation of the drive shaft; a drive mechanism which rotates the drive shaft, the drive mechanism comprising an electric motor and a reduction mechanism, the reduction mechanism having a reduction ratio set to be greater when the valve is under the controlling a small actuation angle only when the valve is under the control of a high operating angle, the reduction mechanism comprising: an output shaft connected to the motor and having an engagement part at its outer periphery ; a movable member engaged with the engaging portion of the output shaft, the movable member moving in the axial direction of the output shaft in accordance with the rotation of the output shaft, the movable member comprising a finger; and a hinged lever having a first end fixed to the control shaft and a second end having a slot, the slot being engaged with the finger, in that the control shaft is rotated by means of the lever articulated in accordance with the axial movement of the movable element, and in that, when the valve is under the control of a small actuation angle, the angle formed between the   articulated lever and the output shaft is decreased.   14. Variable valve control device for an internal combustion engine comprising at least one valve, characterized in that it comprises: a control shaft intended to rotate in accordance with engine operating conditions means for modifying at least the actuation angle of the valve in accordance with the rotation of the control shaft; and means for rotating the drive shaft, these means comprising means for creating a torque and   means for reducing the torque, the latter means having a reduction ratio set to be greater when the valve is under the control of a small actuation angle than when the valve is under the control of an operating angle Student.